1. Field of the Invention
The present invention relates to a multipart packing ring with a number of ring segments and a number of sealing segments which are arranged abutting one another in a sealing manner and so as to form a ring and have radially inwardly curved circumferential surfaces, the ring segments being delimited in the circumferential direction at both ends by first radial end surfaces and an axially protruding shoulder, which is radially inwardly delimited by a tangential sealing surface, being provided on the ring segments in the radially outer region, and also to a pressure packing and a seal comprising a multipart packing ring of this type.
2. The Prior Art
Piston compressors, above all of the double-acting design, require sealing of the crank-side compression space in the cylinder, in which the time-variable (high) cylinder pressure pzyl prevails, along the oscillating piston rod 5. This sealing must typically be carried out relative to the (low) atmospheric pressure pu prevailing in the crankcase. The sealing elements used in a seal 4 of this type are referred to as packing rings 6, 7 and are arranged in what is known as a pressure packing 2 generally consisting of a number of packing rings 6, 7, as illustrated by way of example in a conventional design in FIG. 1. The sealing elements can in this case follow inevitable lateral movements of the piston rod 5 without losing their sealing effect. In order to lengthen the service life and increase the reliability of a pressure packing 2, a plurality of packing rings 6, 7 of this type are connected in series in a pressure packing 2. A plurality of pressure packings are generally lined up one after another in a seal 4. A broad range of configurations of pressure packings 2 and seals 4 of this type are sufficiently well known in the art, for example from GB 928 749 A or U.S. Pat. No. 1,008,655 A.
Packing rings 6, 7 are self-activating seals which for a sufficient sealing effect, i.e. sufficiently little leakage, generally require a certain pressure differential p1−p2 to be sealed (FIG. 1c). The gas pressure in a packing chamber 3 decreases in the gaps to be sealed of a packing ring 6, 7 from the higher level p1 to the lower level p2 in the next packing chamber 3. FIG. 1c shows schematically this reduction in pressure in the sealing gap formed between the packing ring 6, 7 and piston rod 5. This sealing gap has a critical role with regard to the effectiveness of the packing rings 6, 7, as the relative movement of the contact surfaces between the piston rod 5 and rings 6, 7 brings about wear to the packing rings 6, 7. This ring wear generally requires cut ring shapes allowing automatic continuous adjustment of the ring in the event of removal of material from this sealing gap between the ring and piston rod. Radially and tangentially cut rings 6, 7, which are used in pairs in packing chambers of the pressure packing in order mutually to cover the impact gaps which occur in order to compensate for wear, as is schematically illustrated in FIG. 1b, are in this case standard in industry. Radially/tangentially cut ring combinations of this type are single-acting seals which seal only in the direction of the crosshead, whereas in the course of the crank-side reexpansion phase of the piston compressor 1 the radial cuts ensure that no elevated pressure can be enclosed in the packing. As is known, in cut ring shapes, use is conventionally made of hose springs (circumferential springs) 9 which are wound over the outer circumference and press the packing rings 6, 7 against the piston rod 5 even in the pressureless state.
Specifically at elevated pressures, in conventional arrangements, significant extrusion of the packing rings 6, 7 can also occur in the gap formed between the piston rod 5 and packing housing or chamber disc 10. In order to avoid this extrusion as far as possible, additional metallic support rings 8, which do not touch the piston rod 5 in a planar manner, can be used between the ring on the low-pressure side and the chamber disc 10, as disclosed for example in U.S. Pat. No. 3,305,241.
In a combination of a radially and a tangentially cut packing ring, the sealing toward the piston rod is carried out substantially only by the tangentially cut packing ring, the ring segments of which can slide together as a result of the tangential cut guidance in the event of wear and thus maintain the sealing effect. The radially cut packing ring serves substantially just to seal the wear gaps of the tangential packing ring in the axial and radial direction. The radial packing ring wears only until the ring segments abut one another in the circumferential direction. The radially and tangentially cut packing rings thus wear to differing degrees. In order to prevent the radially and the tangentially cut packing ring from rotating relative to each other, which can lead to the wear gaps of the tangentially cut packing ring no longer being covered so that the sealing effect would be lost, a rotation prevention means has to be provided between the rings. A rotation prevention means of this type is generally configured as a pin which is placed in associated recesses in the radially and tangentially cut packing ring. However, as a result of the differing wear to the radially and tangentially cut packing rings, a pin of this type is subjected with continuous wear to ever greater shear stress; this frequently leads to the pin breaking and thus the rotation prevention means and subsequently possibly also the sealing effect of the seal becoming lost.
In the prior art, it has therefore already been proposed to provide not a packing ring combination of a radially and tangentially cut packing ring, but rather merely a single packing ring. In order on the one hand not to lose the required sealing effect relative to the piston rod even under the wear which inevitably occurs and also to be able to ensure an adequate seal also in the axial and radial direction, specially cut packing rings are required for this purpose. Packing rings of this type are known from U.S. Pat. Nos. 2,208,976 and 4,350,349 which describe a six-part packing ring with radially cut ring segments which are held together by a circumferential spring. Radial wear gaps are produced in the circumferential direction between the ring segments. An axially protruding shoulder, which is radially inwardly delimited by a tangential sealing face, is provided on each ring segment to seal said wear gaps. An axial recess is thus formed between these shoulders. In order to seal the wear gaps in the axial and radial direction, sealing segments, which abut the tangential sealing surfaces with tangential end surfaces and cover the wear plate, are inserted into this recess. These sealing segments are held together by a further circumferential spring. Both ring segments and sealing segments rest in this case against the piston rod substantially (apart from necessary wear gaps) over the entire circumference for sealing toward the piston rod. However, the problem with a packing ring of this type is that the ring segments and the sealing segments are subjected to differing wear. The high pressure-side high gas pressure is applied to the ring segments on their outer diameter, whereas less gas pressure, which is reduced by the sealing segments, acts on their inner diameter. As in radially/tangentially cut ring pairs, the ring segments thus wear more rapidly than the sealing segments, as a result of which the entire available ring material is not optimally used in terms of wear. Moreover, these non-uniform rates of wear cause the surface pressure between the tangential sealing surfaces to decrease more and more until sooner or later there is no longer an adequate sealing effect and the leakage through the packing ring becomes unacceptably great.
It is therefore an object of the invention to eliminate the above-described drawbacks of a packing ring of this type, in particular to reduce the wear to a packing ring of this type and the leakage through a packing ring of this type and accordingly to lengthen the service life of a packing ring of this type.